Meshing characteristics and fatigue life analysis of top drive gear transmission system under misalignment

• A model for meshing characteristics and contact fatigue life of shifted helical gears was developed. • Both misalignment directions and types were systematically analyzed for their effects on gear performance. • Misalignment angle has a much greater impact on gear fatigue life than parallel misalignment amount. • Pitch misalignment has a significantly stronger detrimental effect on meshing performance and fatigue life than yaw misalignment. To comprehensively evaluate the service performance of a top drive gear transmission system under complex operating conditions, a mathematical model of the tooth surface for profile-shifted helical gears with comprehensive modifications was derived. A three-dimensional finite element meshing model of the transmission system was developed, and the Brown–Miller–Morrow multiaxial fatigue criterion was applied to systematically investigate the effects of angular and combined misalignments in both pitch and yaw directions on the gear meshing characteristics and contact fatigue life. The results show that misalignment significantly changes the contact pattern and stress distribution of the tooth surface. In the pitch direction, the meshing state is mainly determined by the misalignment angle, while in the yaw direction it is jointly influenced by the misalignment angle and the parallel misalignment amount. Regarding fatigue life, the misalignment angle is the primary factor determining life variation, while the effect of parallel misalignment amount is relatively small. Overall, pitch misalignment leads to a greater deterioration in gear meshing performance and fatigue life than yaw misalignment. The findings of this study provide references for the installation, operation, and maintenance of top drive or other gear transmission systems.